This invention relates to improvements in tow bars for product conveyor systems and, in particular, to a shock-absorbing tow bar for coupling a load-supporting carrier to a powered component of the movable conveyor.
Industrial conveyor systems, including those of the power and free type disclosed herein, typically utilize tow bars between the powered component of the moving conveyor and one or more trailing, load-supporting carriers. Referring particularly to power and free conveyor systems, the powered component is the accumulating trolley on the free track and, when driven, is engaged by a pusher dog projecting from the conveyor chain on the power track. The accumulating trolley is the lead trolley and is connected to a trailing load trolley (or trollies) with a tow bar. Due to the rigidity of the trolley train and carrier assembly, the impact of a pusher dog engaging the accumulating trolley, or the impact of the accumulating trolley striking a stop, is imparted directly to the carrier under tow and may cause the load to shift, damage to the product, or excessive fatigue and wear on the components of the conveyor system.
To alleviate this excessive shock loading, a shock-absorbing link between the driven and towed components of industrial conveyor systems is highly desirable in order to provide a means of controlling the rapid acceleration and deceleration inherent in normal operation of the systems. One such device is an air-type shock absorber utilizing a piston that operates in a pneumatic chamber, an orifice through the piston permitting movement thereof only at a controlled rate. Also, similar devices have been employed of the hydraulic type and have the advantage of improved control due to the incompressibility of hydraulic fluid. An example of the air-type shock absorber is shown and described in U.S. Pat. No. 3,720,172 to Clarence A. Dehne, issued Mar. 13, 1973.
Furthermore, as the hydraulic-type shock absorber is subject to eventual leakage problems which render it totally inoperable and can cause contamination of the plant area occupied by the conveyor, a shock absorber utilizing metallic balls has been employed in an attempt to avoid the disadvantages of air and hydraulic-type shock absorbers. Such a metallic ball device is disclosed in U.S. Pat. No. 5,027,715 to Archie S. Moore et al, issued Jul. 2, 1991 where particulate damping material such as a quantity of ball bearings is positioned in a damping chamber. Acceleration and deceleration cause the bearings to be drawn past a piston through an annular space between the piston and the surrounding wall of the damping chamber. As the bearings become crowded on one side of the piston or the other, the resistance to movement increases. A disadvantage, however, is that over a period of time the piston abrades the surfaces of the balls and can cause them to fracture, thus their ability to roll lessens and the shock absorbing ability is degraded.